Understanding the characteristics of geologic formations and fluids located therein is important for effective hydrocarbon exploration and production. Formation evaluation relies on accurate petrophysical interpretation derived from a diverse set of logging technologies. One such technology, nuclear magnetic resonance (NMR), can be used to estimate formation characteristics such as mineralogy-independent porosity and permeability of rocks, to perform fluid typing and determine fluid volumes, and to estimate fluid characteristics such as viscosity. The design of NMR logging tools is crucial for achieving high performance, high measurement accuracy, and sufficient reliability in extreme high-temperature high-pressure environments. NMR-based tools can be conveyed into a borehole during drilling (e.g., logging-while-drilling) or after drilling (e.g., wireline logging).